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1. Technical Field
The present inventions relate to improvements in the production of hydrocarbons from wells, which intersect fractured subterranean formations. More particularly the present inventions relate to improvements in methods and apparatus for controlling the flowback of particulate materials used in fractured wells during the subsequent production of hydrocarbons from a subterranean formation.
2. Background of the Invention
In the course of treating and preparing subterranean wells for production, frequently particulate materials are used as a proppant in fractures extending outwardly from the wellbore. The term proppant is used herein to refer to the particulate materials used in the hydraulic fracturing process. In fracturing operations, proppant is carried into fractures created when hydraulic pressure is applied to subterranean formations to a point where fractures are developed. Proppant suspended in a fracturing fluid is carried outwardly away from the wellbore within the fractures as the fractures are created and extended with continued pumping. Upon release of pumping pressure, the proppant materials remain in the fractures holding the separated formation faces in an open position forming a channel for flow of formation fluids back to the wellbore.
The proppant is used to keep the propped fractures opened and thus connect the wellbore with the reservoir. However, despite the closure stresses applied on the proppant, high drag forces resulting from high production flow rate can cause proppant to flow out of the fracture and into the wellbore along with the production of oil or gas. Various methods have been attempted to minimize or to stop the flow back of proppant. They include reducing drawdown or production flow rate. Reducing the production flow rate could make operation of the wells uneconomical forcing the operators to abandon the wells.
Coating the proppant at the tail in portion of slurry with resin to transform the proppant pack into consolidate, permeable mass has been used. Various techniques also are described in U.S. Pat. No. 5,492,178, the entire disclosure of which is incorporated herein by reference. Because of the narrow ranges or strict requirements of temperatures and closure stress during curing, most of the treatment with resin coated proppants, especially with the precoated types, can be unreliable resulting in the proppant being produced back immediately or only after a short period after the fracturing treatment.
Other techniques have been used, including releasing treating pressure as soon as the fracturing treatment is completed to allow the fracture to close and the fracturing fluid to flowback, while the proppant is still suspended across the producing portion of the formation. This is known as force-closure technique. The force-closure method often allows a quantity of proppant to be produced back during the operation. However, case histories have indicated that proppant continued to be produced as the wells experience high production flow rates or after they are shut-in and allowed to produce again.
Also, mixing proppant with fibers to create a network between the proppant and the solid strands have been used to minimize proppant movement. U.S. Pat. Nos. 5,330,005, 5,439,055,. 5,551,514 and 5,501,275 disclose methods of incorporation of a fibrous material in the fluid with which the particulates are introduced into the subterranean formation and the entire disclosure of which are incorporated herein by reference. The use of fibers tends to reduce the fracture conductivity, about 30% or more. In some cases, the wells become plugged if a severe loading of fibers is concentrated at one location. In addition, fibers were unsuccessful in controlling proppant flow back for high temperature and high production wells.
Therefore, it is desirable to provide a method and apparatus, which will assist in preventing movement or flowback of proppant into a wellbore without significantly reducing the permeability of the particulate pack and while allowing aggressive production flowback from the well.
The present inventions contemplate an improved method of treating wells and the associated apparatus for controlling and preventing the flowback of particulate into the wellbore during production while increasing the longevity of the well production at an economical level.
In accordance with a preferred embodiment of the invention, an improved method of treating a subterranean formation penetrated by a wellbore is provided comprising the steps of providing a fluid suspension including a mixture of particulate material through the wellbore and depositing the mixture in the formation.
According to one embodiment of the improved method of the present invention, interval(s) of interest in a cased and perforated wellbore are first isolated for example by using packers; completion brine is circulated to clean out the well bore and to make sure the casing perforations are free of debris. Hydraulic fracturing is performed including using a particulate (proppant) that has been gauged against the formation sand to generate propped fractures. The use of coated proppant is optional. The formation fractures are allowed to close by releasing the treating pressure. After the fractures were allowed to closed coiled tubing or the like can be used to circulate proppant from inside the wellbore to the surface. Expandable screens are expanded against the inside of the casing wall (trapping any proppant remaining in the casing against the casing wall) with the expanded screen extending across the perforated intervals to insure all the perforations are covered. The well is then allowed to flow back at maximum flow rate to remove all the fracturing fluid and to ensure that a tight pack of proppant inside all the perforations is formed and to insure the proppant is forced against the outer surface of the screen.
The present inventions, instead of using the screen mesh sizes that stop the formation fines or sand particulates, use screen mesh sizes that are sized to control only the proppant grains. Examples of these expandable screens include screens manufactured from special alloy materials that can withstand erosion caused by high production rate of fines particulate. The packing of proppant inside the perforations and fractures assists in minimizing the impact of fines particulate with the screen. Instead of a straight line, the particles flow in a tortuous path within the proppant pack generating significant drag to reduce its impact against the screen.
The formation fines or sand particulate mostly can be controlled by the sized proppant. However, the smaller particulates can pass through the proppant pack bed. The use of screen mesh as described in this disclosure allows the small particulates to pass through the screen, thus minimizing the buildup or blockage of fines in the pack bed, and allow the proppant, pack to maintain its high conductivity during production.
Surface modifying agent can also be used to coat a thin film on the surface of the proppant during the fracturing treatment to attach the fines particulates and keep them far way from the wellbore and from invading into the proppant pack in the fractures. One example of surface modifying agents includes tackifyer such as described in U.S. Pat. No. 5,775,425, the entire disclosure of which is incorporated herein by reference. Other surface modifying agents such as surfactants and the like could be used.
The use of the expandable screen with well control mesh size to that of proppant provides a reliable method in preventing flow back of proppant into the wellbore, regardless of difficult conditions of the well, such as too high or too low in temperatures, and/or high production flow rate, or the wellbore stability is susceptible to stress cycling during production and shutdown of the well.
The novel features of the inventions are set forth with particularity in the claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.